The present invention relates to dynamoelectric machines and particularly to acyclic (homopolar) generators utilizing liquid metal current collectors.
In acyclic (homopolar) generators the interaction of the component of the excitation magnetic field normal to the plane of the current collectors, i.e., aligned with the path of main generator current between stator and rotor, and the rotor peripheral velocity establishes a voltage which develops circulating currents in both solid brush and liquid metal current collectors. These circulating currents increase open circuit or no load losses by virtue of the resistive losses in the collector tip and brushgear. These circulating currents also produce additional electrical losses in the generator under load conditions by creating a non-uniform current distribution at the collector. The circulating current losses are proportional to the square of both the flux density of the normal magnetic field component and the collector tip velocity. In the case of liquid metal collectors, the additional resistive losses imposed by circulating currents raise the temperature of the liquid metal, and thus its rate of recirculation must be increased to limit this temperature rise to acceptable levels. Excessive liquid metal temperature raises its electrical resistivity and alters its mass density from that to which the structure for containing the liquid metal in the collector region against electromagnetic expulsion forces is normally designed.
A goal of present research and development efforts is to develop smaller, ultra-high current acyclic generators of dramatically increased power density. Increases in the magnetic flux density and/or peripheral velocity of the acyclic machinery are required to develop the necessary generator voltages. Liquid cooled copper armatures and compensating conductors are required to carry the ultra-high currents. This results in larger air gaps between the stator and rotor. The combination of increased flux densities and air gap dimension increases the magnitude of the fringing or leakage fields in the liquid metal collector region. All of these factors contribute to high power densities, as well as increased circulating currents and associated electrical losses in the liquid metal collector region of acyclic generators.
It is accordingly an object of the present invention to provide an acyclic generator having an improved liquid metal current collector.
A further object is to provide an acyclic generator of the above-character having reduced losses associated with the liquid metal current collectors.
A further object of the present invention is to provide an acyclic generator of the above-character wherein circulating currents in the liquid metal current collector region are reduced.
Other objects of the invention will in part be obvious and in part appear hereinafter.